1. Field of the Invention
The present invention relates to a logic emulation system that uses a plurality of component parts on a printed-circuit board to implement equivalent operations of logic circuits in LSIs (large-scale integrated circuits) and computers, thereby emulating the logical operations of these logic circuits.
2. Description of the Related Art
Logic circuits in LSIs and computers are verified traditionally by resorting to logic simulation and through trial manufacture of LSI boards. Logic simulation involves, illustratively, the implementation of the operations of the target logic circuit by use of a computer. One disadvantage of such computer-based logic simulation is that, because the simulation setup operates at very low speeds compared with actual logic circuits, verification takes more time as the scope of the logic circuit in question increases. Where an LSI board is to be produced for trial, several weeks are often required to wire and arrange the LSIs on the board. Thus, it is practically impossible to produce such test setups repeatedly for verification purposes. For this reason, logic emulation for circumventing the above deficiencies of the prior art is drawing increased attention.
Logic emulation utilizes a plurality of component parts mounted on a printed-circuit board to implement equivalent operations of the logic circuits in LSIs and computers. The LSI board setup is operated at a speed close to that of the actual logic circuit for verification. FIG. 2 shows a conventional logic emulation system.
In FIG. 2, design data 110 on the target LSI are input through a workstation 100. In this example, the target LSI is assumed to comprise input/output pins 111 through 116 and gates 121 through 124.
A compiler 130 reads LSI design data and generates therefrom LSI mapping data 140 and PGA (programmable chip array) connection data 150. These two kinds of data are used to produce a programmable gate array (PGA1) 141 and a programmable gate array (PGA2) 142 for performing the equivalent operations of the LSI, and a programmable interconnect device (PID1) 151 for connecting the PGAs.
When the scope of the gates in the target LSI is small, one programmable chip may be sufficient for mapping the gates. However, gates of greater scopes are generally mapped into a plurality of programmable chips. In the example of FIG. 2, gates 121 and 122 are mapped into the programmable chip 141, and gates 123 and 124 are mapped into the programmable chip 142. In logic simulation, the programmable chips 141 and 142 as well as the programmable interconnect chip 151 are mounted on a printed-circuit board 160. For verification, the mounted parts are operated at a speed close to that of the actual logic circuit.
The logic simulation of the above-described type is discussed illustratively in Nikkei Electronics (the Jun. 22 issue, 1992, No. 557, pp. 203-217).
Logic emulation is used not only for logic verification but also for determining the specifications of the target logic circuit. For example, if the logic circuit includes a cache memory, determining the optimum capacity of that memory is an important decision to make, because the greater the capacity of the cache memory, the higher the probability of the desired data residing in that memory. However, boosting the capacity of the cache memory entails one disadvantage: It takes longer to transfer necessary data from main memory to the cache memory if the latter does not have the required data. This means that the capacity of the cache memory needs to be determined optimally in view of the application in which the target logic circuit is to be used. Utilizing logic emulation allows the performance of the target logic circuit to be measured while its cache memory is being varied in capacity until an optimum cache memory capacity is obtained.
Against such a background, the above-described prior art has a major disadvantage: When logic simulation is used to verify the logic of a particular logic circuit or to determine its specifications, even a simple logical change requires modifying the original design data (net list) and, correspondingly, remapping, rearranging and rewiring the programmable chips on the printed-circuit board. This leads to increasing man-hours and longer periods required for developing logic circuits. The same disadvantage is also experienced illustratively in cases where the capacity of the cache memory and observation signals need to be changed.
Another disadvantage of the prior art is that, because of their slow operating speeds, rewritable programmable chips used as PGAs are not fit for logic circuit emulation at desired speeds.
Although FIG. 2 shows an example in which the logic emulation system is composed of programmable chips, logic circuit emulation is also available by use of integrated circuits that are not programmable. The latter case, however, requires altering the connections between parts on the printed-circuit board since some parts on the printed-circuit board need to be added or removed, and/or wiring patterns need to be cut and jumper wires added where necessary. These steps also add to the growing man-hours.